Understanding Sleep:

       We now know that our brains are very active during sleep. Moreover, sleep affects our

daily functioning and our physical and mental health in many ways that we are just beginning to

understand.

       Nerve-signaling chemicals called neurotransmitters control whether we are asleep or awake

by acting on different groups of nerve cells, or neurons, in the brain. Neurons in the brainstem, which

connects the brain with the spinal cord, produce neurotransmitters such as serotonin and norepinephrine

that keep some parts of the brain active while we are awake. Other neurons at the base of the brain begin

signaling when we fall asleep. These neurons appear to "switch off" the signals that keep us awake.

Research also suggests that a chemical called adenosine builds up in our blood while we are awake and

causes drowsiness. This chemical gradually breaks down while we sleep.

     During sleep, we usually pass through five phases of sleep: stages 1, 2, 3, 4, and REM

(rapid eye movement) sleep. These stages progress in a cycle from stage 1 to REM sleep, then the

cycle starts over again with stage 1. We spend almost 50 percent of our total

sleep time in stage 2 sleep, about 20 percent in REM sleep, and the remaining 30 percent in the other stages.

Infants, by contrast, spend about half of their sleep time in REM sleep.

     During stage 1, which is light sleep, we drift in and out of sleep and can be awakened easily. Our eyes

move very slowly and muscle activity slows. People awakened from stage 1 sleep often remember

fragmented visual images. Many also experience sudden muscle contractions called hypnic myoclonia,

often preceded by a sensation of starting to fall. These sudden movements are similar to the "jump"

we make when startled. When we enter stage 2 sleep, our eye movements stop and our brain waves
(fluctuations of electrical activity that can be measured by electrodes) become slower, with occasional
bursts of rapid waves called sleep spindles. In stage 3, extremely slow brain waves called delta waves
begin to appear, interspersed with smaller, faster waves. By stage 4, the brain produces delta waves
almost exclusively. It is very difficult to wake someone during stages 3 and 4, which together are called
deep sleep. There is no eye movement or muscle activity. People awakened during deep sleep do not
adjust immediately and often feel groggy and disoriented for several minutes after they wake up. Some
children experience bedwetting, night terrors, or sleepwalking during deep sleep.
      When we switch into REM sleep, our breathing becomes more rapid, irregular, and shallow, our
eyes jerk rapidly in various directions, and our limb muscles become temporarily paralyzed. Our heart rate
increases, our blood pressure rises, and males develop penile erections. When people awaken during REM
sleep, they often describe bizarre and illogical tales — dreams.
      The first REM sleep period usually occurs about 70 to 90 minutes after we fall asleep. A complete
sleep cycle takes 90 to 110 minutes on average. The first sleep cycles each night contain relatively short
REM periods and long periods of deep sleep. As the night progresses, REM sleep periods increase in length
while deep sleep decreases. By morning, people spend nearly all their sleep time in stages 1, 2, and REM.
      People awakened after sleeping more than a few minutes are usually unable to recall the last few
minutes before they fell asleep. This sleep-related form of amnesia is the reason people often forget telephone
calls or conversations they’ve had in the middle of the night. It also explains why we often do not remember
our alarms ringing in the morning if we go right back to sleep after turning them off.

Hey!!!Wake up. Don't fall asleep after reading all these. :-)

Some more to go.....

How Much Sleep Do We Need?

         The amount of sleep each person needs depends on many factors, including age. Infants generally
require about 16 hours a day, while teenagers need about 9 hours on average. For most adults, 7 to 8
hours a night appears to be the best amount of sleep, although some people may need as few as 5 hours
or as many as 10 hours of sleep each day. Women in the first 3 months of pregnancy often need
several more hours of sleep than usual. The amount of sleep a person needs also increases if he or she has
been deprived of sleep in previous days. Getting too little sleep creates a "sleep debt," which is much like
being overdrawn at a bank. Eventually, your body will demand that the debt be repaid. We don’t seem to
adapt to getting less sleep than we need; while we may get used to a sleep-depriving schedule, our judgment,
reaction time, and other functions are still impaired.
Who sleeps?
Reptiles, birds and mammals all sleep. That is, they become unconscious to their surroundings for periods
of time. Some fish and amphibians reduce their awareness but do not ever become unconscious like the
higher vertebrates do. Insects do not appear to sleep, although they may become inactive in daylight or
darkness.

By studying brainwaves, it is known that reptiles do not dream. Birds dream a little. Mammals all dream
during sleep. Fun fact - cows can sleep while standing up but they only dream if they lie down! Horses
sleep while standing.

Different animals sleep in different ways. Some animals, like humans, prefer to sleep in one long session.
Other animals (dogs, for example) like to sleep in many short bursts. Some sleep at night while others
sleep during the day.

Wow!!! I think I will stop with this and continue later.....
Actually the thought of getting something about sleep in my website was stimulated by my tedious
lab work. I was so tired today and wanted to go home and hit the bed, but had some more work. To keep
myself awake, I decided to do something interesting and at the sametime useful. So came up with this.....;-)